The present disclosure relates to an organic electro luminescence (EL) display panel and a method for producing the organic EL display panel, the organic EL display panel being composed of organic EL elements which rely on the electroluminescence of an organic material.
As the display panel for the display apparatus such as digital television, an organic EL display panel having organic EL elements arranged in a matrix pattern on a substrate has recently put to practical use.
In the organic EL display panel, a light-emitting layer of each organic EL element and an organic EL element adjoining thereto are separated from each other by an insulation layer composed of an insulating material. By contrast, the organic EL display panel for color display has organic EL elements each composed of sub-pixels emitting red (R), green (G), and blue (B) colors, such that the adjoining sub-pixels of RGB combined together constitute the unit pixel for color display.
The organic EL element has a basic structure in which a light-emitting layer containing an organic light-emitting material is disposed between paired electrodes. To drive the organic EL element, the paired electrodes are energized so that the light-emitting layer emits light as the result of recombination of holes and electrons injected thereinto.
There is an organic EL element of top emission type having an element structure in which a pixel electrode, an organic layer (including a light-emitting layer), and a common electrode are sequentially formed on a substrate. The light-emitting layer emits light which is reflected by the pixel electrode made of a light-reflecting material and radiates upward through the common electrode made of a light-transmitting material.
The common electrode is usually formed all over the substrate. This structure poses a problem of voltage drop that occurs across the common electrode having a high electrical resistance at a part far from a power supply unit. This voltage drop results in an insufficient current supply, which in turn decreases the light-emission efficiency and eventually causes uneven luminance.
In order to address this problem, there has been proposed an idea of providing an auxiliary electrode that reduces the resistance of the common electrode (see Japanese Patent Laid-open No. 2002-318556, for example). It discloses a structure composed of the auxiliary electrode and the pixel electrode which are formed on the same level, with the auxiliary electrode and the pixel electrode being electrically isolated from each other but being electrically connected to the common electrode.